Comparison · Feldspar Group vs Metamorphic Rocks
Feldspar vs Marble
Feldspar and Marble are easy to confuse. Feldspar is harder (Mohs 6–6.5) than Marble (Mohs 3.5), so Feldspar will scratch Marble and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Feldspar and Marble
- Feldspar is harder (Mohs 6–6.5) than Marble (Mohs 3.5), so Feldspar will scratch Marble and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
- Hold a thin edge to the light: Feldspar is Transparent to translucent, Marble is translucent.
- They overlap in pink, gray, and green, but Feldspar also comes in clear and Marble also comes in white and black.
Feldspar vs Marble properties
| Property | Feldspar | Marble |
|---|---|---|
| Type | Feldspar Group | Metamorphic Rocks |
| Mohs hardness | 6–6.5 | 3.5 |
| Luster | Vitreous to pearly | vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | translucent |
| Specific gravity | 2.55–2.76 | 2.7 |
| Crystal system | Monoclinic to Triclinic (depending on species) | varies |
| Common colors | White, Pink, Gray, Green (amazonite), Colorless | White, Gray, Pink, Green, Black |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $5–$500+ |
Which is more valuable?
Marble is usually the more valuable of the two: a typical collector specimen runs about $50 against $20 for Feldspar, and premium Marble can reach $500 or more.
About Feldspar
Feldspar is not a single mineral but a group of related aluminosilicate minerals, comprising the potassium feldspars, orthoclase, microcline, and sanidine, and the plagioclase series running from albite to anorthite, together making up roughly 60 percent of Earth's crust by volume. All share a similar framework silicate structure, two cleavage directions near 90 degrees, and moderate hardness, but differ in composition, color, and crystal system. As the most abundant mineral group on the planet, feldspar defines granite, basalt, gneiss, and countless other rock types.
About Marble
Marble is a metamorphic rock composed of recrystallized carbonate minerals. It has been used for sculpture and architecture since ancient times.
Feldspar vs Marble FAQ
Is Feldspar the same as Marble?
No. Feldspar is a feldspar group while Marble is a metamorphic rock. Feldspar is harder (Mohs 6–6.5) than Marble (Mohs 3.5), so Feldspar will scratch Marble and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
How can you tell Feldspar from Marble?
Feldspar is harder (Mohs 6–6.5) than Marble (Mohs 3.5), so Feldspar will scratch Marble and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Hold a thin edge to the light: Feldspar is Transparent to translucent, Marble is translucent. They overlap in pink, gray, and green, but Feldspar also comes in clear and Marble also comes in white and black.
Which is harder, Feldspar or Marble?
Feldspar is harder: Mohs 6–6.5 against Mohs 3.5 for Marble.
Which is more valuable, Feldspar or Marble?
Marble is usually the more valuable of the two: a typical collector specimen runs about $50 against $20 for Feldspar, and premium Marble can reach $500 or more.
